In wire or die bonders used for the assembly of semiconductor packages, substrates for mounting electronic devices are transported and indexed along a conveyor of a substrate transportation apparatus for pattern recognition, alignment of the substrate and bonding of wires or dice onto the substrates. One conventional way of transporting a substrate is by supporting it using several indexers along a guide rail. A substrate transportation apparatus 100 as illustrated in FIGS. 1 A to 1 C utilizes a conventional motion sequence which transfers a substrate 102 between two indexing devices. An input indexer 106 and an output indexer 108 are aligned along a guide rail 104 to relay the substrate 102 linearly. The substrate 102 is transferred from the input indexer 106 to the output indexer 108 approximately midway between the input end and the output end of the guide rail 104.
FIG. 1A shows a window clamp 110 which is located at a bonding position along the guide rail 104. Both the input indexer 106 and the window clamp 110 are closed against the guide rail 104 to clamp against the substrate 102 which has been loaded at the input end of the guide rail 104. The output indexer 108 is located downstream along the guide rail 104 and is kept open in a standby position to receive the substrate 102. When the substrate 102 is held at the window clamp 110, die bonding is carried out at a die bonding position. After the substrate 102 has been further indexed and reaches the output indexer 108, the output indexer 108 clamps onto the substrate 102 as shown in FIG. 1B. At the same time, the input indexer 106 opens to release the substrate 102 which is now supported by the window clamp 110 and the output indexer 108. The output indexer 108 continues to index the substrate 102 towards the end of the guide rail 104 for offloading a bonded substrate 102 as in FIG. 1C, while the input indexer 106 is open and stands by to receive another substrate 102 for indexing along the guide rail 104.
Such a conventional indexing apparatus requires the opening and closing of the input and output indexers 106, 108 and the window clamp 110. Time is wasted for these additional motions and the machine's throughput is affected. Furthermore, transferring the substrate 102 from the input indexer 106 to the output indexer 108 may introduce positional errors to the substrate 102 since the transfer requires each input indexer 106 and output indexer 108 to open and close for releasing or clamping onto the substrate 102 as explained above. Therefore, re-adjustment of the substrate 102 to correct any positional errors that are introduced is necessary after each transfer. Placement compensation by pre-inspection is also required at the die bonding position along the guide rail 104.
One prior art assembly implementing multiple indexers for the transportation of a substrate is described in Japanese Publication No. 2006-156444 entitled “Assembly Device And Transport Device/Method of Workpiece”. The assembly uses two pick-and-place transporting arms for transporting substrates between workstations. Thus, this assembly encounters the above problems and disadvantages since transfer of a substrate between indexers is required. It is thus desirable to devise a substrate transportation apparatus for transporting a substrate effectively without introducing positional errors during the transportation process.